Change NumericGradeEarned to decimal in edfi.Grade

Nebraska is implementing Standards Based Grading. As such, grades might need to have a decimal value (like 1.5, 2.0, etc.). However, NumericGradeEarned in edfi.Grade (Core) currently has a data type of INT. As more projects implement Standards Based Grading, it might make since to consider changing the data type of NumericGradeEarned to decimal (9,2) instead of INT.